The invention relates to the formation of hydrocarbon fractions from petroleum and non-petroleum feedstocks.
As is known to those skilled in the art of petroleum recovery and refining, crude oil is a complex mixture of hydrocarbons that varies in composition depending upon its source. It is widely accepted that crude oil has its origin in plant and animal matter that has been subjected to heat and pressure for millions of years. For most industrial uses, a portion of the crude oil having similar boiling points and viscosity is used, rather than a particular chemical species from the crude. The portions of crude oil separated by boiling point are known as fractions, and the process of separation is known as fractionation. Hydrocarbon fractions, and hydrocarbon fractionation, are well known in the field of petroleum refining.
In simplest form, fractionation involves the selective distillation of petroleum crude into its component parts based upon the boiling temperature of those components parts. Definitions of the fractions vary amongst producers, however one definition is:
FractionBoiling Range (° C.)Number of Carbon Atomsnatural gas <20C1 to C4petroleum ether20-60C5 to C6Gasoline 40-200C5 to C12, but mostly C6 to C8Kerosene150-260mostly C12 to C13fuel oils>260C14 and higherLubricants>400C20 and aboveasphalt or cokeresiduepolycyclicSee, J. G. Speight, The Chemistry and Technology of Petroleum (2007). Each fraction has its own utility, however some fractions are more valuable than others. For example the gasoline fraction may sell for $2.00/gal wholesale while fuel oil sells for $1.50/gal wholesale. Currently, the gasoline fraction is most valuable, however increasing worldwide demand for aviation and diesel fuel makes the kerosene fraction nearly as valuable as the gasoline fraction.
The value spread between the various fractions drives the petroleum refining industry. Various techniques are known to those of ordinary skill in the art for converting low value fractions to higher value fractions. These techniques may include cracking, hydrogenation, and reforming, among others. Cracking refers to breaking long carbon-chain petroleum molecules into shorter carbon-chain molecules. Hydrogenation refers to the addition of molecular hydrogen across one or more carbon-carbon double bonds to produce higher value products. For example, benzene may be hydrogenated to cyclohexane. Reforming refers, generally, to processes that produce higher-value, branched hydrocarbons, such as isoparaffins, from lower value hydrocarbons, such as straight-chain paraffins. Reforming processes can include both cracking and hydrogenation processes.
The petroleum industry relies heavily on catalysts to decrease the temperatures and pressures needed to drive various conversion processes. Catalysts useful in the industry include palladium, platinum, nickel, cobalt, tungsten, iron, and alloys containing these metals. For some processes, catalysts allow a substantial reduction in thermal energy requirements, thereby saving natural gas and electricity costs. However, the catalysts are typically quite expensive, and most lose their effectiveness over time. Once a catalyst has lost its effectiveness, it must be reconditioned or replaced. In many cases, recharging a catalyst results in lost productivity for the conversion process.